kernel/task_work.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/spinlock.h>
   3 #include <linux/task_work.h>
   4 #include <linux/tracehook.h>
   5
   6 static struct callback_head work_exited; /* all we need is ->next == NULL */
   7
   8 /**
   9  * task_work_add - ask the @task to execute @work->func()
  10  * @task: the task which should run the callback
  11  * @work: the callback to run
  12  * @notify: send the notification if true
  13  *
  14  * Queue @work for task_work_run() below and notify the @task if @notify.
  15  * Fails if the @task is exiting/exited and thus it can't process this @work.
  16  * Otherwise @work->func() will be called when the @task returns from kernel
  17  * mode or exits.
  18  *
  19  * This is like the signal handler which runs in kernel mode, but it doesn't
  20  * try to wake up the @task.
  21  *
  22  * Note: there is no ordering guarantee on works queued here.
  23  *
  24  * RETURNS:
  25  * 0 if succeeds or -ESRCH.
  26  */
  27 int
  28 task_work_add(struct task_struct *task, struct callback_head *work, int notify)
  29 {
  30         struct callback_head *head;
  31         unsigned long flags;
  32
  33         do {
  34                 head = READ_ONCE(task->task_works);
  35                 if (unlikely(head == &work_exited))
  36                         return -ESRCH;
  37                 work->next = head;
  38         } while (cmpxchg(&task->task_works, head, work) != head);
  39
  40         switch (notify) {
  41         case TWA_RESUME:
  42                 set_notify_resume(task);
  43                 break;
  44         case TWA_SIGNAL:
  45                 if (lock_task_sighand(task, &flags)) {
  46                         task->jobctl |= JOBCTL_TASK_WORK;
  47                         signal_wake_up(task, 0);
  48                         unlock_task_sighand(task, &flags);
  49                 }
  50                 break;
  51         }
  52
  53         return 0;
  54 }
  55
  56 /**
  57  * task_work_cancel - cancel a pending work added by task_work_add()
  58  * @task: the task which should execute the work
  59  * @func: identifies the work to remove
  60  *
  61  * Find the last queued pending work with ->func == @func and remove
  62  * it from queue.
  63  *
  64  * RETURNS:
  65  * The found work or NULL if not found.
  66  */
  67 struct callback_head *
  68 task_work_cancel(struct task_struct *task, task_work_func_t func)
  69 {
  70         struct callback_head **pprev = &task->task_works;
  71         struct callback_head *work;
  72         unsigned long flags;
  73
  74         if (likely(!task->task_works))
  75                 return NULL;
  76         /*
  77          * If cmpxchg() fails we continue without updating pprev.
  78          * Either we raced with task_work_add() which added the
  79          * new entry before this work, we will find it again. Or
  80          * we raced with task_work_run(), *pprev == NULL/exited.
  81          */
  82         raw_spin_lock_irqsave(&task->pi_lock, flags);
  83         while ((work = READ_ONCE(*pprev))) {
  84                 if (work->func != func)
  85                         pprev = &work->next;
  86                 else if (cmpxchg(pprev, work, work->next) == work)
  87                         break;
  88         }
  89         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
  90
  91         return work;
  92 }
  93
  94 /**
  95  * task_work_run - execute the works added by task_work_add()
  96  *
  97  * Flush the pending works. Should be used by the core kernel code.
  98  * Called before the task returns to the user-mode or stops, or when
  99  * it exits. In the latter case task_work_add() can no longer add the
 100  * new work after task_work_run() returns.
 101  */
 102 void task_work_run(void)
 103 {
 104         struct task_struct *task = current;
 105         struct callback_head *work, *head, *next;
 106
 107         for (;;) {
 108                 /*
 109                  * work->func() can do task_work_add(), do not set
 110                  * work_exited unless the list is empty.
 111                  */
 112                 do {
 113                         head = NULL;
 114                         work = READ_ONCE(task->task_works);
 115                         if (!work) {
 116                                 if (task->flags & PF_EXITING)
 117                                         head = &work_exited;
 118                                 else
 119                                         break;
 120                         }
 121                 } while (cmpxchg(&task->task_works, work, head) != work);
 122
 123                 if (!work)
 124                         break;
 125                 /*
 126                  * Synchronize with task_work_cancel(). It can not remove
 127                  * the first entry == work, cmpxchg(task_works) must fail.
 128                  * But it can remove another entry from the ->next list.
 129                  */
 130                 raw_spin_lock_irq(&task->pi_lock);
 131                 raw_spin_unlock_irq(&task->pi_lock);
 132
 133                 do {
 134                         next = work->next;
 135                         work->func(work);
 136                         work = next;
 137                         cond_resched();
 138                 } while (work);
 139         }
 140 }